The present invention relates to a drilling vessel with a drilling tower or a drilling mast for drilling in the earth""s surface from the vessel, for example, for oil or gas.
In the prior art, it is known to drill in the earth""s surface from a drilling vessel, for example, for oil or gas. The drilling is generally carried out by means of a bit mounted on the drilling string. Such a drilling string is constructed on the drilling vessel from separate drilling string elements. Adding drilling string components at the top side means that the drilling string can extend farther and farther at the bottom side of the drilling vessel in the direction of the seabed. Despite the fact that the drilling string can move freely through the water, feeding the drilling string to the seabed takes a relatively long time. Furthermore, the greater the depth to which drilling must be carried out, the more time is needed to construct the drilling string and to move the drilling string in the direction of the seabed.
If the bit fixed to the end of the drilling string becomes blunt during the drilling, the drilling string in its entirety must be raised to the drilling vessel. That means that the drilling string has to be dismantled into drilling string elements during the raising operation. This operation generally also takes a long time.
In view of the enormous investment which is necessary for the construction of a drilling vessel, the pressure becomes ever greater to increase the efficiency of these drilling vessels. The lengthy construction and subsequent dismantling of the drilling string is a major obstacle to improvement of the efficiency of such vessels.
It is an object of the present invention to provide a device by means of which considerable time can be saved during the construction and dismantling of the drilling string.
That object is achieved by an auxiliary tower or auxiliary mast placed next to the drilling tower or drilling mast, and a clamp carriage which is fixed so that it is movable between a first position near the drilling tower or drilling mast and a second position near the auxiliary tower or auxiliary mast, the clamp carriage having at least one gripping clamp for clamping the drill string.
It is advantageous here for the clamp carriage to comprise a clamp block with at least two gripping clamps, and for the clamp block to be fixed rotatably to the clamp carriage.
It is preferable to use masts instead of towers, because in this way the pipes can be transferred from a central pipe storage point, using a single facility, to the drilling mast and the auxiliary mast (and vice versa).
The presence of the auxiliary mast on the drilling vessel makes it possible to prepare a second drilling string while the first drilling string is being constructed, or when drilling is being carried out with the first drilling string, or when the first drilling string is being raised. There is no need to wait with the construction of the second drilling string until the moment when the first drilling string has been raised in its entirety to the drilling vessel. With the clamp carriage it is possible, when the bottom side (the bit) of the first drilling string has been raised from the drill hole, to grip the first drilling string with the clamp carriage, in which the second drilling string constructed in the meantime is also clamped. The second drilling string is then placed above the drill hole by a rotating movement. The second first drilling string can then be taken below the auxiliary mast by the clamp carriage, in order to raise the string and dismantle it further.
The great advantage of this is that a minimum amount of time is lost in raising the first drilling string. The first drilling string in fact only has to be raised over the length of the drilled hole, and as soon as the drill hole is clear the second drilling string can be placed in the drill hole. The first drilling string can be dismantled while drilling is already being carried out with the second drilling string. That means that with the drilling vessel according to the present invention relatively little time is lost in constructing drilling strings and dismantling them again.
The advantages described above also apply when constructing a casing or a riser from the drilling vessel. Just as in the case of the drilling string, the casing (lining of the top part of the drill hole) and the riser (sheath of the drilling string from the seabed to the drilling vessel) is constructed from separate elements situated on the vessel. During the construction and possible dismantling of the casings and/or risers, the presence of the auxiliary tower or auxiliary mast can produce a substantial time gain, just as in the case of the construction and dismantling of the drilling string.
The drilling vessel according to the present invention is further improved if the auxiliary tower or auxiliary mast is connected by means of a brace to the drilling tower or drilling mast.
The towers or the masts are subject to acceleration forces. That means that the towers or the masts have to be made relatively heavy, in order to be able to absorb such acceleration forces. If a physical connection is now made between the drilling tower or drilling mast and the auxiliary tower or auxiliary mast, a much more rigid construction is obtained, in which construction the towers or masts themselves can be made relatively light.
The drilling vessel according to the present invention is also improved if the vessel comprises means for supplying drilling string elements to and discharging them from the drilling mast, the supply and discharge means for the drilling string components being placed in such a way that drilling string components can be supplied with them from a central storage facility both for the drilling mast and for the auxiliary mast.
The great advantage of this is that instruments needed for use of the drilling mast, such as a gripping arm for passing over the drilling string components, can be used both for the drilling mast and for the auxiliary mast. That means that the use of the auxiliary mast does not require any additional investment in these instruments. The additional investment required for construction of the auxiliary mast consequently remains limited.
It is also advantageous for the masts to be attached to the drilling vessel by means of hinges.
If the drilling vessel is also being used for laying pipelines, as soon as the drill hole is clear it is advantageous for the angle between the longitudinal axis of the masts or the towers to be adjustable relative to the horizontal. The lines (for example rigid steel lines or flexible lines) are then sunk with the aid of the drilling mast and/or drilling mast and auxiliary mast. If the drilling vessel reaches a depth at which the lines to be laid can no longer leave the drilling vessel vertically at the bottom side, the drilling mast can be set in a slanting position, in order to be able to continue the sinking of the lines. A further advantage of the xe2x80x9chingedxe2x80x9d attachment of the mast(s) here is that the mast can be dismantled in a simple manner and transferred to another vessel.
It is advantageous for the drilling mast and the auxiliary mast to be connected to the vessel by means of cylinders.
The advantage of this is that the rotation of the drilling mast and the auxiliary mast is relatively simple to set.
It is also advantageous for the drilling mast to comprise attachment means for attaching a tensioner.
That means that, for example, when flexibles are being laid a tensioner can be set on the drilling mast, in order to improve the laying of the lines.